1. Field of the Invention
The invention relates to a thermometer, and more particularly to a thermal radiometer that detects thermal radiation.
2. Description of the Related Art
Thermal radiometer is a device used to determine the temperature of a heat source after receiving heat radiated by the heat source. There are a variety of applications, from thermal imaging systems (infrared thermal imaging systems, night vision scope, physiological examinations) to celestial observation, etc. All of these applications require the thermal radiometer to have high absorption and high sensitivity.
FIG. 1 shows a conventional thermal radiometer 1 that includes a base 11, and a heat measuring unit 12 disposed on the base 11. The heat measuring unit 12 includes a thermal layer 121 made of thermo-sensitive material and formed on the base 11, and two signal arms 122 extending respectively from two end portions of the thermal layer 121, wherein the two signal arms 122 are provided for signal input and signal output, respectively. When measuring, an initial input voltage is inputted into one of the two signal arms 122, and an initial output voltage corresponding to the initial input voltage can be measured from the other one of the two signal arms 122. When the thermal layer 121 receives the heat radiated by the heat source, the resistance value thereof changes, and a sense output voltage can be measured from the changes in output voltage of the other one of the two signal arms 122. The sense output voltage is then, for example, amplified or converted to determine the temperature of the heat source.
As the thermal radiometer 1 described above has the base 11 being in direct contact with the thermal layer 121, heat conduction will influence the sensitivity of the thermal radiometer 1. There are some references directed to improving the sensitivity of the thermal radiometer. For example, Taiwanese Patent Number 514723 (Micro-bridge Structure for a Bolometer, Method of Fabricating the Same onto a Substrate and Transducer) and Taiwanese Patent Number 561249 (High-absorption wide-band pixel for bolometer arrays) suggest respective technical schemes of micro-bridge structure and platform body suspended by supporting arm, in which the base is not in direct contact with the thermal layer to lower thermal conduction and thus improve the sensitivity of the thermal radiometer.
Although the technical schemes such as the micro-bridge structure or the platform body suspended by the supporting arm offer some improvement on the problem of thermal conduction between the base and the thermal layer that influences the sensitivity of the thermal radiometer, the thermal layer is still affected by heat coming from the environment when receiving the radiated heat of the heat source, which means the heat detected by the thermal radiometer is relative to the environmental temperature. Therefore, although the conventional thermal radiometer may have higher sensitivity, the accuracy of the temperature detected for the heat source still needs improvement for higher precision applications.